Against this background, an object of the invention is to specify a motor vehicle electrical axle assembly of compact overall dimensions, which is cost-effective to produce.
In the case of the aforementioned electrical axle assembly, this is achieved in that at least one of the shafts comprises a bearing journal, which is radially supported in an axial bearing bore of a shaft coaxial therewith.
This measure, whereby two coaxial shafts are connected to a shaft arrangement via a bearing journal and a bearing bore instead of being arranged independently side by side, affords considerable advantages in terms of overall space and cost savings, particularly in respect of the bearing support.
Combining the coaxial shafts in one shaft arrangement furthermore makes it possible to simplify the housing of the electrical axle assembly.
The term bearing bore is here taken to mean any common form of axial depression, which may have different diameters over the axial length.
The electrical axle assembly can in this case be used for an axle of a motor vehicle, for example a rear axle, a front axle or for both axles. One single such electrical axle assembly is sufficient to drive a motor vehicle. This axle assembly may also be combined with a further drive device on the other vehicle axle, however, in order to create an all-wheel drivetrain. The other drive unit here may comprise a conventional internal combustion engine.
The object is thereby achieved in full.
According to a preferred exemplary embodiment the bearing journal is supported in the bearing bore by at least one needle-roller bearing.
In general terms this bearing may be any other bearing that is designed for relatively low differential speeds between the bearing journal-shaft and the bearing bore-shaft. This is because whilst the vehicle is underway these two shafts generally rotate synchronously and in mobile operation differential speeds occur relatively rarely, for example when cornering. Consequently no elaborate bearings are needed for the relative bearing support between the bearing journal-shaft and the bearing bore-shaft.
The bearing journal is preferably supported in the bearing bore by two bearings, in particular needle-roller bearings, separated by an axial interval from one another.
According to a further preferred embodiment the bearing journal-shaft has a shoulder section, an axial bearing being arranged between the shoulder section and the bearing-bore shaft.
In other words, the bearing journal-shaft and the bearing bore-shaft are axially supported against one another via an axial bearing such as an axial needle-roller bearing or roller bearing.
The axial bearing is designed to absorb axial forces between the two coaxial shafts. One single such axial bearing is here sufficient for the shaft arrangement.
According to a further preferred embodiment the shaft arrangement comprising the bearing journal-shaft and the bearing bore-shaft is supported on a housing by two shaft bearings.
Although the two shafts of this shaft arrangement generally serve to drive different driving wheels independently of one another, these shafts through the bearing journal/bearing bore arrangement form a common shaft arrangement, which can be supported on a housing by means of just two shaft bearings. This consequently obviates the need to support each of these shafts by two shaft bearings of their own. Accordingly the number of relatively expensive shaft bearings for this shaft arrangement can be kept to a minimum. Where needle-roller bearings are used for the relative bearing support between the bearing journal-shaft and the bearing bore-shaft, these are relatively inexpensive, since for one thing these have to transmit smaller loads and for another they only transmit lower differential speeds.
The shaft bearings serve in particular to absorb radial forces and generally also axial forces.
It is furthermore advantageous if the input shafts are each connected to the output shafts via a gear set, the gear sets being arranged symmetrically about a longitudinal axis.
It is also advantageous here if the bearing journal extends into the bearing bore at least up to the gear set which is located on the bearing bore-shaft.
A large axial overlap is thereby achieved between the bearing journal and the bearing bore, so that the bearing bore-shaft and the bearing journal-shaft act together as a unified shaft arrangement.
For this reason it is also preferable for the bearing journal to extend into the bearing bore at least up to a shaft bearing which serves to support the bearing bore-shaft on a housing.
By doing this, forces exerted on the bearing bore-shaft by the bearing journal in this area can be transmitted in a radial direction directly into the shaft bearing. This obviously applies all the more if the free end of the bearing journal is supported inside the bearing bore by means of a needle-roller bearing or some other bearing which is substantially radially aligned with to the outer shaft bearing.
According to a further preferred embodiment a parking position gear is fixed to each of the coaxial shafts.
There is sufficient space available in an axial direction, particularly if the coaxial shafts, as a common shaft arrangement, are supported on a housing by just two shaft bearings, to provide such parking position gears on the shafts. The arrangement of the input shafts moreover affords favourable scope for the accommodation of a parking mechanism.
It is particularly advantageous in this case if the parking position gear is in each case arranged between a shaft bearing, which serves to support the input shaft on a housing, and a gear wheel which is connected to the output shaft.
This embodiment presents itself particularly when the input shafts are each connected to the output shafts via an intermediate shaft.
It is generally feasible for each of the input shafts to be connected to the output shafts via a single transmission stage.
It is particularly advantageous, however, if the input shafts are in each case connected via a first transmission stage to a respective one of a first and a second intermediate shaft, these shafts in each case being connected to the respective output shafts via a second transmission stage.
In this embodiment it is possible to distribute the requisite overall transmission ratio to two transmission stages. Consequently the gear wheels, particularly those arranged on the output shafts, may have a relatively small diameter, so that restrictions on the overall space typically existing in this area can be complied with.
It is furthermore advantageous overall if the input shafts are connected to the output shaft via at least a first and a second gear set, the first gear set and the second gear set being of symmetrical design about a longitudinal axis, in such a way that axial forces resulting from the tooth engagements cancel each other out.
A symmetrical arrangement of the gear sets is accordingly also taken to mean that any helical toothing systems of the gear wheels are symmetrical, like those in a herringbone gearing, and the axial forces due to the helical toothing engagement cancel each other out, at least when transmitting the same torque to the two driving wheels.
It is also advantageous overall if the axle assembly has a two-part housing, the two housing parts of which are substantially symmetrical about a longitudinal axis.
Such a strictly two-part configuration is possible, particularly if each of the coaxial shafts of the electrical axle assembly is in each case nested one inside the other through a bearing journal/bearing bore, so that the shaft assemblies thus created are in each case supported on the housing by just two shaft bearings. If each of the coaxial shafts were to be supported by two shaft bearings of its own, a middle housing bearing plate would have to be provided for the adjacent shaft bearings of the two coaxial shafts, so that the housing would have to be of at least three-part construction.
It is furthermore advantageous overall if the bearing journal and the bearing bore are of a conically tapering design.
This allows the shafts to be optimized for the load stresses, particularly in an axial direction. In other words it serves to prevent excessive stresses occurring due to the flexural loads at certain points.
It is particularly advantageous here if the outside diameter of the bearing journal in the area of its point of origin is equal to the outside diameter of the bearing bore-shaft at the point where this is supported on a housing by means of a shaft bearing.
A compact overall shaft arrangement comprising the bearing journal-shaft and the bearing bore-shaft can thus be created not only in an axial direction but also in a radial direction.
According to a further preferred embodiment the bearing bore has an oil feed aperture in the area of the free end of the bearing journal.
Oil can be delivered through the oil feed aperture into the space between the bearing bore and the bearing journal for the bearing(s) situated therein, in particular the needle-roller bearings arranged therein. If the bearing bore and the bearing journal are of a tapered design narrowing towards the free end of the bearing journal, the centrifugal forces acting in the intermediate space can be used to lubricate all bearings for the relative support of the bearing bore-shaft and the bearing journal-shaft, that is to say not only the needle-roller bearings serving as radial bearings but also any axial bearing between the bearing bore-shaft and the bearing journal-shaft.
Overall the electrical axle assembly affords at least one of the following advantages:
It results in compact dimensions, especially smaller axial intervals and gear diameters. The electrical axle assembly can consequently be used in many applications both on the front axle and on the rear axle.
The absence of a middle housing part means that the housing may comprise just two housing parts.
In terms of construction the main bearing support for the shafts by means of the shaft bearings corresponds to a single drive. This reduces the number of (expensive) shaft bearings.
The bearings for the relative support of the bearing journal-shaft and the bearing bore-shaft experience only the differential speeds between the two drives (for example when cornering). This applies both to the radial bearings and also to the axial bearing(s). These can consequently be embodied as relatively simple needle-roller bearings. This results overall in a simple construction and easy assembly. Moreover there is more overall space available for the parking mechanism components.
It will be obvious that the aforementioned features and those yet to be explained below may be used not only in the particular combination specified but also in other combinations, or individually, without departing from the scope of the present invention.